The present invention pertains to the radio communication art and, more particularly, to a means for coherently recovering a signal received by an antenna array.
Various antenna lens assemblies have been developed for use in the radio communication art. A common application for a radio frequency lens is that of focusing a radio frequency signal received by a multiple antenna array. There, a signal impinging on the array strikes some antennas sooner than others due to the antennas spatial relationship. If the signals received by all antennas are to be combined, time coherency must be restored. It is the function of the lens to provide appropriate time delays to each antenna received signal whereby all signals may be combined in proper time and phase relationship.
The conventional prior art approach to providing the desired time delays is to pass the signals through links of cable serving as delay lines. Such systems have necessarily been costly, bulky and very inflexible. For example, in a multi sectored antenna array it is frequently necessary to alter the phasing relationship among the antennas to direct the array's radiation pattern in various directions. The prior art approach to providing this directive beam lens has included mechanical turntables which sequentially couple transmission lines to the various antennas to thereby provide the desired phasing. Such systems are bulky, costly and relatively unreliable in operation. Moreover, such prior art systems were not capable of both simultaneously beaming in various directions and providing the desired phase coherency.
Another prior art approach to radio frequency lens systems is the use of a transverse electromagnetic wave tuned cavity such as an RKR type lens. Here, antenna signals are fed to probes located within the cavity. The probe location, and the transmission characteristics of the cavity are such that proper combining occurs at receiving probes. Such cavity systems are costly to construct and do not generally require precision in some applications.